Working rollers for applying pressure to a web of material are utilized in a variety of process applications such as for calendering any of various webs, or continuous sheets, of paper, cloth, plastic, etc.; textile carding; gravure; printing; drying; roll coating; and other operations. A common problem associated with the use of such working rollers is maintenance of the desired amount of pressure across the entire width of the web of material. In most cases it is desired to maintain a constant pressure between the working roller and the opposing surface along the entire line of contact between the working roller and the web of material. However, it should be understood that for certain applications it might be desirable to apply variable pressure across the width of the web of material. For example, in calendering or roll coating operations it might be desirable to provide the web of material with edges or margins which are thinner or thicker than the central portion of the web, in which case the pressure between the working roller and the opposing surface, such as a platen or back-up roller, is adjusted to be greater, or lower, at that portion of the line of contact between the working roller and the web which is coincident with the edges of the web. As another example, it might be desirable for aesthetic or other reasons to provide a calendered or roll coated plastic web having a wavy appearance due to a roughly sinusoidally variable thickness across its width.
Even in the simplest situation where it is desired to maintain uniform pressure across the entire line of contact between the working roller and the web, various factors often make it difficult to achieve and maintain the desired amount of pressure across the entire width of the web contacting the working roller. Such factors include, for example, the effect of the weight of the roller, particularly as the length of the roller increases, which causes the roller to bow or deflect longitudinally near its center. Other factors which have an effect on the pressure distribution across the line of contact between the working roller and the web of material include uneven wear of the outer surface of the roll-shell, and temperature variations of the roll-shell along the line of contact between roller and the web. It is now generally recognized that the maintenance of a desired pressure distribution along the entire line of contact between the working roller and the web can be achieved most effectively, particularly for longer rollers, by means of a working roller having internal means for controlling the deflection thereof.
Known means for controlling the deflection or outer contours of a working roller have generally included the provision of one or more hydraulic pressure chambers which are arranged between an outer cylindrical roll-shell and a fixed axle, or the provision of one or more inner rollers attached to a stationary inner beam which can be urged toward the inner wall of an outer cylindrical roll-shell. Such means have generally been designed to provide increased outward deflection along the line of contact between the working roller and the opposing surface between which the web of material passes in order to compensate for longitudinally symmetrical bowing effects attributable to the weight of the roller or to thermal effects at the margins of the web, and thereby achieve or re-establish a constant line of force across the width of the web. One disadvantage with the conventional means for controlling the deflection or contours of the outer cylindrical roll-shell is that they generally do not allow for non-symmetrical adjustments such as at individual zones along the line of contact between the working roller and the web of material interposed between the working roller and an opposing surface where uneven wear or other unpredictable phenomena have caused random localized deflections. Other disadvantages with known means for controlling roller deflection include their inability to allow for adjustments of varying magnitude or direction in adjacent zones along the line of contact between the working roller and the web of material. For example, the known adjustment means have not generally permitted a negative pressure adjustment at a selected portion of the line of contact between a working roller and a web of material interposed between the working roller and an opposing surface while simultaneously allowing for positive pressure adjustments at adjacent areas along the line of contact. Accordingly, the limited deflection controllability provided by known apparatuses is usually insufficient to effectively compensate for unexpected or unpredictable deviations from a desired pressure distribution across the line of contact between the working roller and a web of material interposed between the roll-shell and the back-up roller or other opposing surface, especially when such deviations are asymmetric with respect to the longitudinal mid-point of the roller. Moreover, because the known working rollers having deflection adjustment means are primarily designed to compensate for bowing or other symmetrical deflections and re-establish a uniform pressure distribution across the line of contact between the working roller and the web of material to apply uniform pressure along the width of a web of material, they cannot generally be adjusted or adapted to maintain a desired non-uniform pressure distribution such as when a web having a predetermined transversely varying thickness is desired.
Accordingly, there exists a heretofore unfulfilled need for a working roller with variable deflection control means, wherein greater control of the outer contours of the roll-shell along the line of contact between the working roller and a web of material interposed between the roll-shell and an opposing surface is achievable to compensate for various unexpected and unpredictable deviations from a desired pressure distribution along said line of contact. More specifically, there is a need for such a deflection controllable working roller which is capable of compensating for localized, longitudinally asymmetrical deviations which can often occur, especially after extended use of the working roller. Additionally, a deflection controllable working roller which is adaptable for maintaining a predetermined non-uniform pressure distribution along the line of contact between the working roller and a web of material, for processing a web having a desired non-uniform profile such as to achieve a decorative effect, would be desirable.